textproduct: Albany

WHAT HAS CHANGED

No significant changes were made during this forecast iteration. As in previous, we continued to blend the NBM with its 90th percentile for winds and wind gusts late Friday night through Sunday due to the tendency of the NBM alone to under-forecast them without sufficient incorporation of local terrain influence. Likewise, we also continued to blend NBM with its 25th percentile for temperatures over the same time period to capture the full potential of the cold which will also be significantly influenced by terrain and localized radiational cooling processes.

KEY MESSAGES

1) Periods of light snow showers will bring minor impacts mainly to portions of the Mid-Hudson Valley, Capital District, Upper- Hudson Valley, and northwestern New England late Friday night through Saturday.

2) Widespread, dangerously cold conditions are expected this weekend which will lead to an increased risk of hypothermia and frostbite should proper precautions not be taken to limit exposure.

DISCUSSION

KEY MESSAGE 1...

The next best chance for widespread precipitation continues to be expected late Friday evening through Saturday afternoon with snow showers expected to overspread the region as a result of a clipper system.

By Friday afternoon, an upper-level cyclone will become positioned near the Hudson/James Bay area, extending a neutrally-tilted shortwave trough southward into the Eastern Great Lakes. Just ahead of this main axis, a secondary, weak shortwave embedded within the mean flow aloft will begin to approach the region, likely acting just to increase cloud cover due to its overall lack of moisture and weak forcing. The uncertainty here continues to be allocated to the location and development of an area of weak surface low pressure just ahead of or along the arctic front associated with the primary surface low well to our north, also located near the Hudson/James Bay area. With this being a relatively moisture- starved system already, that increased surface convergence and subsequent lift would certainly help to moisten the column and at least allow some snow showers to begin in portions of the Southern Adirondacks and possibly the Eastern Catskills Friday evening where orographic enhancement due to easterly to southeasterly flow could be sufficient to allow precipitation to reach the ground. Most of the medium- range guidance continues to indicate this area of low pressure developing and sinking far enough south that it does extend into our CWA.

Directly in the wake of the first shortwave comes the second, primary shortwave that looks to deepen as it rotates through our region. Unlike in previous iterations, the area of low pressure along the front no longer looks to undergo cyclogenesis along the New England coast as a response to this deepening aloft, but rather farther to the south and east, deeper in the western Atlantic. Timing of this deepening surface low now also doesn't look to occur until Saturday morning. Still, mildly moist cyclonic flow will force the persistence of snow showers across the region into Saturday morning and possibly the afternoon, especially across higher terrain courtesy of persistent upslope flow. Along with the passage of the shortwave comes that of the arctic cold front, allowing winds to begin shifting to the north-northwest. The steepening pressure gradient with the deepening low off the coast and a building high to the west will intersect an area of increasing low-level frontogenesis along and ahead of the front. This could lead to some isolated snow squalls developing early Saturday morning, though there is not high confidence in this detail of the forecast at this time. Part of the uncertainty relates to the lack of surface instability that is being indicated by the medium-range guidance at this time. Regardless, as previously stated, snow showers will persist into Saturday afternoon before completely scouring out in the face of increasing subsidence in the wake of the front. When all is said and done, snowfall accumulations look to range from ~0.5" to 1.5" with localized higher amounts up to 2 in the Southern Adirondacks. Slippery travel conditions are therefore possible as a result and therefore caution should be taken when going about any weekend activities Saturday.

KEY MESSAGE 2...

Confidence remains unwaveringly high in a prolonged period of dangerously cold conditions consuming eastern New York and western New England in the wake of the arctic front associated with the aforementioned system. Sufficient mixing into anomalously cold (nearly 2-3 STDEVs below normal) lower levels of the atmosphere will translate to well below normal surface temperatures that will, in and of themselves, be brutally cold. But this same mixing into a 30-40kt LLJ at 925 hPa in addition to the cyclogenesis of the clipper low and building high to the west significantly steepening the pressure gradient across our region, will make for gusty winds, therefore making already cold temperatures feel bone- chilling.

The probabilities discussed in days previous haven't changed significantly, owing to the continued high confidence in not only the extent but the occurrence of the cold. As with the previous update, the passage of the front looks to occurr early to mid-morning Saturday, which greatly reduces the likelihood of Friday night's temperatures and wind chills tapping into the "dangerous" category. However, Saturday, Saturday night, and Sunday night are the three coldest periods of this arctic outbreak and therefore have the highest likelihood of eventual Extreme Cold Watches/Warnings and/or Cold Weather Advisories. That said, Monday night, too, could also be rather cold, though with winds continuing to decline, it is less likely that cold weather headlines, if any are needed, would be widespread. The latest NBM Minimum Temperature QMD probabilities for subzero ambient temperatures across eastern New York and western New England range from ~50-100% Saturday night; ~30-100% Sunday night; and ~10-70% Monday night. The latest LREF probabilities for apparent temperatures (wind chill values/"feels-like temperatures) less than -10 range from ~20-90% Saturday during the day; ~80-100% Saturday night; ~40-90% Sunday night; and ~20-60% Monday night.

The coldest period in this outbreak will definitely be Saturday night when apparent temperatures fall as low as the upper 10s to mid 30s. It is important to note that frostbite can occur within 30 minutes of exposure to such conditions if proper attire are not worn. Additionally, damage to infrastructure can also occur if proper care to heating systems are not taken. Please be sure to take the proper precautions to be safe amid this outbreak.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

VFR conditions are expected mainly the next 24 hours ending 1800 UTC/Thu for KGFL/KALB/KPOU/KPSF. Some high MVFR stratocumulus will continue prior to 2100 UTC for KPSF with cigs in the 2.5-3.0 kft AGL range. Improvement to VFR flight conditions is expected thereafter for KPSF with sct stratocumulus and some high clouds increasing. A short-wave trough will move across the region tonight with an increase of mid and high clouds especially north of KPOU. Expect some low VFR stratocumulus to move into KALB/KPSF/KGFL after 12Z/Thu. The winds will be west to northwest 7-12 KT with a few gusts around 20 KT at KALB/KPSF this afternoon. Winds will go light to calm tonight with weak ridging ahead of the short-wave trough. The winds increase from the west/northwest at 5-10 KT late tomorrow morning.

Outlook...

Thursday Night: No Operational Impact. NO SIG WX. Friday: No Operational Impact. NO SIG WX. Friday Night: High Operational Impact. Breezy. Likely SHSN. Saturday: Moderate Operational Impact. Windy With Gusts To 34 kts. Chance of SHSN. Saturday Night: Moderate Operational Impact. Windy With Gusts To 31 kts. NO SIG WX. Sunday: No Operational Impact. NO SIG WX. Sunday Night: No Operational Impact. NO SIG WX. Monday: No Operational Impact. NO SIG WX.

ALY WATCHES/WARNINGS/ADVISORIES

CT...None. NY...None. MA...None. VT...None.